The Effect of Nonvertical Shear on Turbulence in a Stably Stratified Medium

Direct numerical simulations were performed in order to investigate the evolution of turbulence in a stably stratified fluid forced by nonvertical shear. Past research has been focused on vertical shear flow, and the present work is the first systematic study with vertical and horizontal components of shear. The primary objective of this work was to study the effects of a variation of the angle θ between the direction of stratification and the gradient of the mean streamwise velocity from θ=0, corresponding to the well-studied case of purely vertical shear, to θ=π/2,corresponding to purely horizontal shear. It was observed that the turbulent kinetic energy Kevolves approximately exponentially after an initial phase. The exponential growth rate γ of the turbulent kinetic energy K was found to increase nonlinearly, with a strong increase for small deviations from the vertical, when the inclination angle θ was increased. The increased growth rate is due to a strongly increased turbulence production caused by the horizontal component of the shear. The sensitivity of the flow to the shear inclination angle θ was observed for both low and high values of the gradient Richardson number Ri, which is based on the magnitude of the shear rate. The effect of a variation of the inclination angle θ on the turbulence evolution was compared with the effect of a variation of the gradient Richardson number Ri in the case of purely vertical shear. An effective Richardson number Rieff was introduced in order to parametrize the dependence of the turbulence evolution on the inclination angle θ with a simple model based on mean quantities only. It was observed that the flux Richardson number Rifdepends on the gradient Richardson number Ri but not on the inclination angle θ

Compact International Experiences: Expanding Student International Awareness Through Short-Term Study Abroad Courses With Substantial Engineering Technical Content

Compact International Experience (CIE) courses are investigated as a suitable tool to raise student international awareness while retaining substantial engineering technical content. These courses were developed due to a strong student desire for engineering international studies as well as a drive by the home institution for internationalization of the curriculum. The efficacy of such courses is described through experiences gained from delivering two distinct three-semester-unit engineering elective courses in a three-week time frame in France and Australia. While each of these courses, Topics in Fluid Mechanics and Advanced Electronic Circuit Design, focused on its technical content, the desire for student understanding of the cultural environment and the impact of engineering solutions from a global and societal viewpoint were strong driving factors for each. Assessment validates the hypothesis that CIE courses can successfully deliver substantial engineering technical content while providing an enriching international experience to students

On the Structure and Dynamics of Sheared and Rotating Turbulence: Direct Numerical Simulations and Wavelet Based Coherent Vortex Extraction

The influence of rotation on the structure and dynamics of sheared turbulence is investigated using a series of direct numerical simulations. Five cases are considered: turbulent shear flow without rotation, with moderate rotation, and with strong rotation, where the rotation configuration is either parallel or antiparallel. For moderate rotation rates an antiparallel configuration increases the growth of the turbulent kinetic energy, while the parallel case reduces the growth as compared to the nonrotating case. For strong rotation rates decay of the energy is observed, linear effects dominate the flow, and the vorticity probability density functions tend to become Gaussian. Visualizations of vorticity show that the inclination angle of the vortical structures depends on the rotation rate and orientation. Coherent vortex extraction, based on the orthogonal wavelet decomposition of vorticity, is applied to split the flow into coherent and incoherent parts. It was found that the coherent part preserves the vortical structures using only a few percent of the degrees of freedom. The incoherent part was found to be structureless and of mainly dissipative nature. With increasing rotation rates, the number of wavelet modes representing the coherent vortices decreases, indicating an increased coherency of the flow. Restarting the direct numerical simulation with the filtered fields confirms that the coherent component preserves the temporal dynamics of the total flow, while the incoherent component is of dissipative nature

Surface Water Quality: Contaminants and Treatment

Extensive population growth and urbanization is affecting surface water quality and infrastructure across the globe. Urbanization was boosted by the advancements of infrastructure for water, which allows treatment and transport of water through large distances from their original surface water sources such as lakes, rivers, and streams. A major concern of the rapid changes experienced by urban areas is the ecological impacts on surface water due to associated anthropogenic processes. Activities such as the overconsumption and extraction of surface water have negatively affected the quality and quantity of those sources. In addition, discharge of treated wastewater may impact the quality of the water source. Prevention of overexploitation and contamination of surface water resources is typically related to community culture and available technologies. Examples of this can include community appreciation of water resources and efforts to limit water usage in households and industries, by implementing new water technologies. This project looks into the effect of knowledge and technology on the quality of surface water sources and the use of those resources. This information is used to devise a comprehensive analysis of water conservation efforts on the quality and quantity of surface waters in Southern California and Israel. The project will involve research by the University of San Diego and Azrieli College of Engineering in Jerusalem

A Comparison of the Microcirculation in Rat Spinotrapezius Muscle and Muscle Fascia

The microcirculation in rat spinotrapezius muscle and muscle fascia is investigated using a computational approach. The simulations are based on a realistic microvascular network structure obtained from microscope observations and consider both blood rheology and vessel elasticity. An improved model for the apparent viscosity of blood is developed to take the shear thinning nature of blood into account. Capillary bundles of muscle tissue are composed of vessels that mainly follow the direction of muscle fibers. In muscle fascia, however, the capillary vessels form a mesh like network without a preferred direction. This structural difference leads to significant differences in the microcirculation. In the muscle fascia, vessel length, velocity, and shear rate follow a lognormal distribution. In muscle, however, the data does not support a lognormal distribution. For both networks, the hematocrit follows an approximately normal distribution

On the Structure and Dynamics of Sheared and Rotating Turbulence: Anisotropy Properties and Geometrical Scale-Dependent Statistics

This study is based on a series of nine direct numerical simulations of homogeneous turbulence, in which the rotation ratio f/S of Coriolis parameter to shear rate is varied. The presence of rotation stabilizes the flow, except for a narrow range of rotation ratios 0\u3cf/

Free Your Mind-Unlock Your Inner Creativity

Creativity is a major factor in many careers, subjects, and disciplines. Although many people first assume engineering to be a field of study that does not require any creativity, it is actually an essential tool for successful engineers. The mark of a truly accomplished engineer is the ability to problem-solve effectively; in other words, to generate creative solutions. Although the goal as engineers is to become more creative throughout one’s career, is it even possible to gain creativity? Is creativity an innate quality, or a learned one? Since the engineering process demands creativity, we looked into how creativity can be improved, and how exactly it is used in the engineering design process. We surveyed engineering freshman students to determine how they view themselves and how important they think creativity is in relation to engineering. We then conducted research to see what creativity means to different people, how one can improve creativity according to various theories, and how creative processes have been used in past engineering projects. We presented this information to all sections of a second-semester engineering freshman course and surveyed the students at the beginning and end of the lecture to see how their views changed. We evaluated this data to discover if students perceive creativity as learned or innate and how it affects their idea on engineering. The students showed an improvement in awareness of the importance of creativity in engineering and how often it is used. Many did not change their opinion of themselves with regard to creativity but some actually ranked themselves lower after the presentation, presumably because they realized the extent of how creative some people are, especially in regard to engineering. The other data we analyzed was student responses to short questions. We asked students what qualities they associate with creative people and the most commonly used words were “thinks outside of the box,” “innovative,” “confident,” and “open minded.” We also asked what the best techniques for improving creativity within a group are. The most common answers were “different backgrounds,” “different ideas,” “being comfortable,” and “diversity.” These answers mirrored the overall message we attempted to portray throughout our presentation to a fair degree

A Comparison of the Turbulence Evolution in a Stratified Fluid With Vertical or Horizontal Shear

The evolution of homogeneous turbulence in a stratified shear flow is studied using direct numerical simulations. Vertically stably stratified flows with uniform vertical shear and with uniform horizontal shear are considered and compared. The Richardson number is varied to include unstratified and strongly stratified cases. For a given value of the Richardson number, the turbulent velocity and density fluctuations were found to be significantly larger in the horizontal shear case due to an increased turbulence production rate that is not directly influenced by buoyancy. Eddy viscosity and eddy diffusivity coefficients are about an order of magnitude larger in the horizontal shear case. Volume visualization shows internal wave development in the strongly stratified cases with both vertical or horizontal shear. A vanishing buoyancy flux, however, is observed in the vertical shear case only. In decaying vertical shear cases, the Ozmidov scale restricts the size of vertical overturns. However, such a restriction was not observed in horizontal shear cases

Scalar Transport and Mixing in Turbulent Stratified Shear Flow

In this study, the evolution of the velocity field and scalar concentration fields in stably stratified shear flow is studied using direct numerical simulations. Two cases with vertical mean shear and horizontal mean shear are compared. In both cases, the growth of the turbulent kinetic energy weakens as the Richardson number is increased. However, the horizontal shear case shows a stronger growth of the turbulent kinetic energy than the vertical shear case for a given Richardson number. The ordering of the velocity components was found to change from streamwise \u3e horizontal \u3e vertical in the vertical shear case to streamwise \u3e vertical \u3e horizontal in the horizontal shear case. The fluctuation level of a passive species variable with a vertical mean gradient was observed to be stronger in the horizontal shear case. The ratio of the vertical turbulent eddy diffusivity to the horizontal turbulent eddy diffusivity was found to be larger in the horizontal shear case